Introduction

Noise is unwanted sound that can cause impairments or damage to health. This article describes the problem of noise exposure at work places and the risk to health and safety of the workers. Different noise effects as hearing loss, physiological effects, work-related stress and increased risk of accidents are explained. The main sectors having noise problems are identified, including the music and entertainment sector. The noise assessment in accordance with the European Directive 2003/10/EC and the relevant measurement standards are explained. Different strategies of noise control are presented: noise control by design, choosing quiet machines, measures on the transmission path and organisational measures.

Health effects

Outline

Millions of employees in Europe are exposed to noise at work and all the risks this can entail. About 7% suffer from work related hearing difficulties [1]. Noise-induced hearing loss is one of the most prevalent recognised occupational diseases in the EU [2]. While hearing loss is most obviously a problem in industries such as manufacturing, construction and agriculture, it can also be an issue in the entertainment sector, such as orchestras and discotheques.
Because communication and hearing are affected by noise exposure the probability of accidents increases at relevant workplaces. Even relatively low noise levels can cause problems in the workplace because the noise is annoying and disturbing. Noise can give rise to stress reactions that have a detrimental effect on the ability to concentrate and on productive efficiency [3][4]. These problems are recognised for instance in call centres and sectors such as education and healthcare.

Hearing loss

Chronic hearing loss

Noise exposure at the work place over many years may lead to irreversible hearing loss if daily sound exposure levels reach or exceed 85 dB(A) [5].

The incidence of noise-induced hearing loss can be described as follows:
Following exposure to noise, for example during the working shift, the sensitivity of the ear is temporarily reduced. This can be demonstrated audiometrically as a temporary shift in the hearing threshold (temporary threshold shift). The affected individual has the sensation of his or her ears being blocked. The hearing may gradually recover if it is given a sufficiently long break. This may take hours or even days. If however the recuperation period is not sufficient for the sense of hearing to recover completely and partial deafness from the previous day is still present at the beginning of the next shift, a metabolic deficit (metabolic fatigue) remains which over a longer period causes the hair cells of the inner ear to die [6][7][8]. The consequence of this is a permanent hearing loss. Subsequent exposure to noise causes the symptoms to be worse over time.

Experience shows that the sense of hearing degrades with age, even in the absence of any particular adverse exposure to noise (age-related hearing loss – presbycusis) [5][9]. There is no cast-iron physiological rule that ageing must be accompanied by hearing loss. On average however, older people can generally be expected to have lower hearing sensitivity, particularly at higher frequencies. In this case, the damage can primarily be found in the inner ear. In addition, ageing may be accompanied by stiffening of the mechanism of the middle ear. This in turn also has an influence at low frequencies.

Noise-induced hearing loss is a particularly insidious condition, since it occurs virtually unnoticed by the affected individuals. They feel no pain and initially can communicate easily because hearing loss begins at higher frequencies around 4,000 Hz. Under continued exposure to noise, the hearing loss gradually spreads into lower frequency ranges including those of speech. As a result, the affected individuals have difficulty following a conversation, particularly in acoustically unfavourable environments and with strong background noise. The drop in hearing sensitivity with increasing age intensifies this problem. Ultimately, those who have suffered hearing loss are barely able to converse even in quiet environments, and easily become increasingly isolated from their fellow human beings. Hearing aids can compensate only partially for the hearing loss.

Acute hearing loss (acoustic shock)

In addition to the hearing loss from long-term noise exposure (metabolic fatigue), direct structural damage to the hair cells may occur if a certain exposure threshold is excessed [6][10][11]. In this case the hair cells break off as a result of excessive mechanical strain. This is described as traumatic or acute hearing loss.

A risk of acoustic shock exists under exposure to extremely high noise pulses with peak sound-pressure levels LCpeak of 155 dB and higher. E.g. gunshots, explosions or the burst of a truck tyre can cause such high noise impulses. A single noise event of this kind may be sufficient to create permanent damage to an unprotected ear (i.e. in the absence of hearing protection) [12][13][14].

Other causes of hearing loss

Noise is however not the only possible cause of hearing loss. Other reasons may be stiffening of the mechanism of the middle ear (otosclerosis), degenerative processes in the inner ear, exacerbated or premature ageing, infections, head injuries, certain forms of medication, and ototoxic substances (e.g. work-related industrial chemicals) [15].

Tinnitus

Noise-induced hearing loss is often accompanied by tinnitus. Tinnitus is usually described as a ringing noise or whistling sound which sufferers perceive in their ears. It may be a continuous or an intermittent sound. One type of tinnitus arises from muscle spasms that cause clicks or crackling around the middle ear. Tinnitus can result from different other causes than noise, e.g. neurological damage, ear infections, nasal allergies. Tinnitus may cause irritability, fatigue and sometimes even clinical depression [16].

Physiological effects, work-related stress

Employees may be distracted and irritated at work even by relatively low sound-pressure levels, upwards of approximately 30 dB(A). The causes include air-conditioning systems, PC cooling fans, and often conversations at adjacent workplaces. In the first instance, mental responses such as annoyance, tension and nervousness are observed [3][4][17][18]. The reactions vary widely from person to person and are linked not only to the level of the noise exposure, but also to the complexity of the task performed, the individual's attitude to the noise, and their instantaneous physical and mental constitution.
Exposure to noise above approximately 60 dB(A) is shown to lead to vegetative responses, for example increased respiratory and cardiac frequency, increased blood pressure and higher stress hormone values. These are clearly stress responses which, in conjunction with exposure over many years to other occupational stresses, may harm the cardiovascular or gastrointestinal systems [19][20]. There is strong evidence that noise is associated with hypertension, evidence concerning cardivascular diseases is weaker [21].
Disruptive noise exposure and the associated stress responses have an impact upon work performance and this impact increases as a function of the complexity of the work to be performed [18]]. The influence of the noise can be compensated for in the short term by greater concentration and effort. Work stages are checked more frequently or simple solutions sought. Owing to the associated effort and fatigue however, lower productivity and a higher error rate must be anticipated. For this reason, investments in noise abatement measures may pay off economically even at relatively low sound pressure levels, since they lead to higher productivity and quality.

Increased risk of accidents

Ultimately, personal performance also has an influence upon occupational safety. More frequent accidents must therefore be anticipated under exposure to noise, owing to incorrect behaviour and startle responses. In addition, the disruption to speech communication in noisy environments and the poor perception of warning signals lead to an increased accident risk; employees may for example easily miss a colleague's warning shout or an approaching fork-lift truck [18].

Relevant noise sources

Noise and the corresponding annoyance is a problem in every industry sector, even in office environments. The problem of noise induced hearing loss is most likely to be found in industries such as manufacturing, construction and agriculture. The risk of suffering noise induced hearing loss can be illustrated by the diagnosed cases of work-related hearing loss. In Germany noise in the workplace is the most common work-related health hazard. In 2011 6,125 new cases of work-related hearing loss were recorded in industrial and public service occupations [22]. Figure 1 presents the relative percentage of diagnosed cases of work-related hearing loss in 2011 with respect to the industry sectors.

For many years the metal and woodworking sectors ranked highest with a percentage of about 44% in 2011, followed by construction with about 20%. Together the mining, minerals and chemical industries have a percentage of about 11%, while precision engineering, printing and textiles have a percentage of about 7%.
Besides these workers in industry, agriculture and public service the members of armed forces such as military and police personal are known to have high noise exposures particularly from the use of weapons. These may produce very high peak sound pressure levels LpCpeak of about 160 dB and more [23][24].
In the music and entertainment sectors the sound exposure is not an unwanted secondary effect but to some degree expected by the audience. Nevertheless, this sound can cause a risk to the hearing of musicians, technical staff, performers and other workers who work in entertainment venues – and hearing is a very important tool for the musician. There are various studies on the sound levels experienced by orchestral musicians that confirm percussionists, brass and woodwind players and the musicians who are positioned in front of these instruments are at risk [25][26]. Average sound levels for the musicians in symphony or opera orchestras were measured as between 80 and 100 dB(A). Noise levels in discotheques and night clubs may be even higher, up to 115 dB(A) [27][28][29].
In the field of music and entertainment the implementation of the 2003 noise directive is difficult because the classical concept of noise control at the source or wearing hearing protectors is often not accepted [30].
In order to provide a comparison of noise levels at different workplaces figure 2 presents noise levels reported in industry and construction and in the entertainment sector.

Figure 2: Noise levels at different noise sources

Source: Analysis of different measurements of IFA and literature

Noise assessment in accordance with the EU-Directive 2003/10/EC

EU-Directives with relevance to noise at work

The Noise Directive 2003/10/EC [31] (2003 noise directive) is an individual directive within the meaning of Article 16 of Framework Directive 89/391/EEC [32]. It defines the minimum health and safety requirements regarding the exposure of workers to the risks arising from noise. This Directive replaces the previous Directive 86/188/EEC [33] on the protection of workers from the risks related to noise exposure at work and it introduces lower exposure action levels and new limit values in order to avoid hearing loss of the workers.
Under the 2003 noise directive the employer is obliged to assess and, if necessary, measure the noise exposure of the workers. The defined exposure action values require different preventive measures when these values are exceeded (see section "Prevention measures based on the EU-Directive 2003/10/EC"). The exposure limit values, after taking account of the attenuation of hearing protection, must not be exceeded.
The noise directive 2003/10/EC should be seen in the context of other directives:

The Framework Directive 89/391/EEC of 12 June 1989 [32] states general principles of prevention and places obligations on employers to guarantee a safe working environment. The employer has to take measures necessary to avoid risks and to evaluate the risks which cannot be avoided. Workers must be provided information and training and are subjected to adequate health surveillance.

The Machine Directive 2006/42/EC of 17 May 2006 [34] lays down essential safety and health requirements of machinery. It requires technical noise reduction at the source and a declaration of noise emission, which has to be part of the instruction manual and of the technical brochures used to sell the machine.

The Council Directive 89/656/EEC of 30 November 1989 on the minimum health and safety requirements for the use by workers of personal protective equipment [35] (PPE directive) provides minimum requirements for the assessment, selection and correct use of hearing protectors (personal protective equipment).

Prevention measures based on the EU-Directive 2003/10/EC

The 2003 noise directive requires an up-to-date assessment of the risks from noise exposure at the workplace [36][37]. The assessment and, if necessary, measurement of noise exposure shall be planned and carried out by competent services at suitable intervals applying objective measuring methods. Considering the actual state of standardization this means, that the measurements should be performed according to the generally recognized standard ISO 9612 [38]. For the risk assessments according the directive the following noise parameters are used:

As a basis for the prediction of the risk and the decision on appropriate prevention measures the noise directive introduces exposure action values. Additionally exposure limit values are defined in order to avoid irreversible damage to workers hearing. The limit values take account of the attenuation provided by individual hearing protectors worn by the workers, that is to say, the limit values correspond to the individual noise exposure of the ear. The defined action values and limit values are listed in table 1.

if, despite of taken measures, exposures above the exposure limit values are detected, the employer shall take immediate action to reduce the exposure to below the limit values.

The particular characteristics of the music and entertainment sectors require practical guidance to allow for an effective application of the provisions laid down in the noise directive 2003/10/EC [31]. Therefore, Member States are invited to develop practical guidelines which would help workers and employers in those sectors to attain the above-named levels.

Noise measurement strategies

The European Directive 2003/10/EC has given the impetus for the revision of the ISO 9612 [38] that specifies the measurement and assessment of occupational noise. This International Standard provides a stepwise approach to determine the noise exposure level LEX,8h as an indicator for the risks from noise exposure at the work place. Optionally the determination of the highest C-weighted peak sound pressure level LC,peak is required.
The procedure according ISO 9612 contains the following steps: work analysis - selection of measurement strategy – measurements - uncertainty calculation.
Three measurement strategies are offered:

task-based measurement: the working shift of a nominal day is analyzed and split up into a number of representative tasks, and for each task separate measurements are taken,

job-based measurement: a number of random samples of sound pressure levels are taken during the performance of particular jobs,

The selection of the appropriate measurement strategy is influenced by several factors such as the complexity of the work situation, number of workers involved, effective duration of the working day, and amount of detailed information required. For further information on the measurement procedure see [38][39].

Noise reduction measures

The Directive 2003/10/EC (Article 5) requires the risks arising from exposure to noise to be eliminated or reduced to a minimum taking account of technical progress and of the availability of measures to control the risk at the source [36][37]. Different noise reduction measures are listed in the directive, such as

noise reduction by technical means,

choose of other working methods,

appropriate maintenance programmes for work equipment,

organisational measures of noise control.

When dealing with noise control at workplaces the information presented in three parts of EN ISO 11690 [40] may be useful for all parties involved. Part 1 is the central document in the series. It defines basic terms and describes the systematic approach to noise reduction in work and office areas. Part 2 deals with various technical measures of noise control. Part 3 describes the sound propagation in a room and the prediction of the noise exposure at work places.

Noise control by design

Since machines can normally be considered the major sources of noise in the workplace, the design of low-noise machines as required by the machinery directive 2006/42/EC [34] is an essential measure to reduce noise at the workplace. The two parts of the standard EN ISO 11688 [41] may assist the machine manufacturers in designing quieter machines:
Part 1 explains the basic model of noise generation in machines distinguishing between airborne, liquid-borne and structure-borne sources. Additionally a comprehensive guidance on how to influence the different sources, transmission paths and radiating surfaces is given.
Part 2 provides an introduction into the physics of low-noise design. In order to quantify the effect of specific noise reduction measures some simple formulas for the physics of noise generation, transmission and radiation are presented.

Noise control by choosing quiet machines

The employer or operator of a machine is usually not in the position to change the fundamental design of the machine and to realise a low-noise machine by himself. But when buying new machinery they can use the noise emission declaration made by the manufacturer under the machinery directive (2006/42/EC) [34]. This declaration on noise emission should help the buyers of machinery identify low noise models, and should give the producers of quiet machines an advantage on the market. Consequently, a low noise emission should become a quality parameter for machines. A machine with a high sound quality would emit less noise and should result in a reduced noise exposure at the workplace.
On the basis of the declared noise emissions the potential customer can choose the machine with the lowest noise emission as intended by the 2003 noise directive [42]. In the implementation of the legal requirement to state the machine’s noise emission according the machinery directive [34] there are often problems, because the noise declaration in many cases is inaccurate or even missing. Furthermore the operating state in real machine use can differ considerably from the measurement conditions prescribed in the measurement standard.

Noise reduction on the transmission path

Noise exposure in work spaces is composed of the sound directly emitted by machines and equipment and of the sound reflected by walls and ceiling. By giving ceiling and/or walls a sound-absorbing surface, it is possible to reduce the reflected sound and thus reduce the noise exposure at the workplaces concerned. It is important to consider room acoustics when planning new work areas, as a retrofit is usually much more elaborate and expensive.
According to the 2003 noise directive, workrooms are to be designed so that the sound propagation conditions conform to the state of technology. Room acoustic parameters are not governed by European Directives, but some national regulations define values which are in accordance with the state of technology. Recommended values are also to be found in EN ISO 11690-1 [40].
Based on EN ISO 11690-1 the following room acoustic quality is required as a function of the room volume (state of technology):

reverberation time Tr < 0.8 s for a room volume < 200 m2

reverberation time Tr < 1.3 s for a room volume < 1,000 m2

Rate of spatial decay per distance doubling DL2 = 3 - 4 dB for a room volume of more than 1,000 m2.

As the fitting of absorbing materials can be extremely costly it is useful to calculate the effect of different room configurations before installation.
Depending on the initial situation, noise reductions of roughly 1 to 6 dB(A) can be achieved in the proximity of machines, and even 10 dB(A) and more at greater distance from the noise sources.

↑DIRECTIVE 89/656/EEC of 30 November 1989 on the minimum health and safety requirements for the use by workers of personal protective equipment at the workplace

↑ 36.036.1EC - European Commission, How to avoid or reduce the exposure of workers to noise at work – non-binding guide to good practice for the application of Directive 2003/10/EC. Office for Official Publications of the European Communities, Luxembourg, 2008. Available at: [2]

↑ European Committee for Standardization, EN ISO 11688: Acoustics – Recommended practice for the design of low-noise machinery and equipment, Part 1: 1998 Planning; Part 2: 2000 Introduction to the physics of low-noise design

↑ European Committee for Standardization, EN ISO 11689: 1996 Acoustics – Procedure for the comparison of noise-emission data for machinery and equipment